1. Field of the Invention
The present invention generally relates to continuously variable transmissions. More specifically, the present invention relates to an improved torque transfer arrangement that transfers torque between shafts and pulleys of such transmissions.
2. Related Art
Continuously variable transmissions (xe2x80x9cCVTsxe2x80x9d) are used to transfer torque from an input shaft to an output shaft. The CVT allows a speed change to occur within the transmission. Thus, the CVT is generally capable of converting input speeds into output speeds that are steplessly variable within a given range.
Recently, these transmissions have been used in the automotive industry for transferring torque between input shafts and output shafts of vehicles employing low horsepower engines. Torque is transferred from an input shaft, through a single input pulley, to a single output pulley and, ultimately, to an output shaft. Some of the CVT drives used in automobiles have used a steel segmented V-belt operating between the two axially adjustable steel pulleys. The pulleys open and close to change effective diameters, which movement changes the pulley size ratio between the input shafts and the output shafts changes. Pulley movement is usually caused by a combination of springs and hydraulics.
Operational qualities of the CVT are well known in the automotive industry, including their shortcomings. Continuous research and development efforts are being expended to extend the capabilities of the basic belt and adjustable pulley concept because of the perceived advantages to be realized over more traditional transmissions now in production.
Applicant has determined that one of the shortcomings of some current CVT drives involves large and intermittent frictional loads experienced within the interface between the shaft and the hub of the moveable pulley half. As discussed above, the moveable pulley half moves relative to the shaft to change the effective diameter of the pulley. In one arrangement, loose ball bearings are installed in axial races formed between mating surfaces of the shaft and the hub of the moveable pulley half. The ball bearings are designed to allow torque to be transferred between the shaft and the hub of the moveable pulley half while reducing frictional loading between the shaft and the hub during sliding movement of the hub relative to the shaft.
This linear-type ball bearing arrangement is acceptable but does not always perform as desired. For instance, if the balls do not stay next to one another in the race or do not roll uniformly along the race between each extreme of travel, the balls may skid or otherwise increase friction between the hub and the shaft. In other words, because the balls are loose, in a momentary absence of torque such as encountered during deceleration accompanied by vehicle turning, or other influences the balls may roll unrestrained out of the preferred position to either extreme of the race. If torque is then reapplied to the transmission with the balls out of position, one or more balls will not be able to roll during movement of the moveable pulley half. Thus, the balls skid within the race and the frictional load may be unnecessarily increased. This increased load may lead to rapid deterioration of transmission components and cause erratic movement of the moveable pulley during ratio changes.
In addition, the scaling up to production of the linear-type ball bearing arrangement reveals an additional drawback. The axially oriented races, formed in mating surfaces of the shaft and the hub, require a high degree of manufacturing precision to be properly aligned between the shaft and the hub after assembly. Usually three sets of balls and races are used. The races generally comprise mating channels formed on the outer diameter of the shaft and on the inner diameter of the moveable pulley. The two channels form a race that carries the balls. The balls transfer torque between the two components through the two channels. The goal is to have each set of balls and races carry one-third of the torque load during axial displacement of the pulley relative to the shaft while side loads are preferably avoided between the two components. Thus, in an ideal arrangement, all six channels have to be accurately formed in a xe2x80x9ctruexe2x80x9d position with minimal manufacturing tolerances. For instance, if one of the channels is out of true, that channel may carry more or less of the torque relative to the other channels such that disadvantageous side loads may result. The side loads can adversely affect performance of the transmission. Accordingly, unwanted sliding friction may be increased as a result of unavoidable manufacturing tolerances encountered in the real world.
In addition, once manufactured, the axial races cannot be adjusted to accommodate any manufacturing imperfections. Accordingly, either the components are correctly dimensioned or the components have an improper fit and are discarded after quality control. Thus, many scrapped components may have to be manufactured to build a single transmission, thereby increasing the price of the associated transmission.
Moreover, inspection of an assembled transmission to assure that the proper alignment has been achieved is exceedingly difficult. Because the channels generally form an enclosed race, the race is an internal component that may not be easily inspected after assembly. Thus, the misalignment may not be identified until problems develop within the transmission during actual use.
Therefore, one aspect of the present invention involves a moveable pulley for a variable speed transmission. The pulley comprises a fixed sheave half and a moveable sheave half. The moveable sheave half is capable of axial movement relative to the fixed sheave half. At least one bearing is one of the fixed sheave half and the moveable sheave half. At least one race is connected to the other one of the fixed sheave half and the moveable sheave half. The bearing is capable of rotation about an axis that extends generally normal to an axis of rotation of the pulley. The race comprises two generally parallel side walls that extend in a direction generally defined by the axis of rotation of the pulley. The side walls define a channel. The bearing is positioned within the channel such that the bearing can axially translate within the channel and such that torsion forces on the pulley are transferred between the bearing and the walls in either direction of rotation.
Another aspect of the present invention involves a continuously variable speed transmission comprising a drive shaft supporting a drive pulley, a driven shaft supporting a driven pulley and a belt extending between the drive pulley and the driven pulley. At least one of the drive pulley and the driven pulley comprises a moveable sheave half and a stationary sheave half. The stationary sheave half is fixed to a corresponding one of the drive shaft and the driven shaft and the moveable sheave half is capable of axial movement in a direction defined by a rotational axis of the corresponding one of the drive shaft and the driven shaft. At least one bearing is connected to one of the fixed sheave half and the moveable sheave half. At least one race is connected to the other one of the fixed sheave half and the moveable sheave half. The bearing is capable of rotation about a bearing axis that extends generally normal to the rotational axis of the corresponding one of the drive shaft and the driven shaft. The race comprises two generally parallel side walls extending in a direction generally defined by the rotational axis of the corresponding one of the drive shaft and the driven shaft. The side walls define a channel. The bearing is positioned within the channel such that the bearing may axially translate within the channel and such that torsion forces are transferred between the bearing and the walls in either direction of rotation.
A further aspect of the present invention involves a variable speed transmission comprising an input shaft supporting two input pulleys. The two input pulleys each comprise a fixed input sheave half and a moveable input sheave half. An effective diameter of each of the input pulleys is adjustable by axial movement of the moveable input sheave half relative to the fixed input sheave half. The moveable input sheave halves are interposed between the fixed input sheave halves along the input shaft. A synchronizing member connects the two moveable input sheave halves such that the effective diameters of the two input pulleys are maintained substantially equal by the synchronizing member. At least one of the moveable input sheave halves is dynamically keyed to the corresponding fixed input sheave half by a torque transmission mechanism. The torque transmission mechanism comprises a bearing that rotates about an axis generally normal to a rotational axis of the input shaft and a race that is defined by a pair of walls that extend in directions generally parallel to the rotational axis of the input shaft. The bearing is capable of translation within the race while forces are capable of transmission between at least one of the pair of walls and the bearing.
An additional aspect of the present invention involves a variable speed transmission comprising an output shaft supporting two output pulleys. The two output pulleys each comprise a fixed output sheave half and a moveable output sheave half. An effective diameter of each of the output pulleys is adjustable by axial movement of the moveable output sheave half relative to the fixed output sheave half. The fixed output sheave halves are interposed between the moveable output sheave halves along the output shaft. A differential connects the two fixed sheave halves to the output shaft. At least one of the moveable output sheave halves is dynamically keyed to the corresponding fixed output sheave half by a torque transmission mechanism. The torque transmission mechanism comprises a bearing that rotates about an axis generally normal to a rotational axis of the output shaft and a race that is defined by a pair of walls that extend in directions generally parallel to the rotational axis of the output shaft. The bearing is capable of translation within the race while forces are capable of transmission between at least one of the pair of walls and the bearing.
Another aspect of the present invention involves a variable speed transmission comprising an input shaft supporting a first input pulley and a second input pulley. The first input pulley comprises a first fixed input sheave half and a first moveable input sheave half. The second input pulley comprises a second fixed input sheave half and a second moveable input sheave half. An effective diameter of the first input pulley is adjustable by axial movement of the first moveable input sheave half relative to the first fixed input sheave half. The first input pulley includes an adjustable stop surface. The adjustable stop surface is selectively secured and selectively repositionable along the input shaft at a location that limits axial movement of the first moveable input sheave half relative to the first fixed input sheave half.
A further aspect of the present invention involves a method of assembling a variable speed transmission. The method comprises assembling at least one adjustable input pulley to an input shaft and assembling at least one adjustable output pulley to an output shaft. A vacuum is applied both to the input shaft to open the input pulley and to the output shaft to open the output pulley. The belts are positioned over the input pulley and the output pulley. The input shaft and the output shaft are then secured in a transmission case and the vacuum is released.
Yet another aspect of the present invention involves a variable speed transmission comprising an input shaft supporting two input pulleys and an output shaft supporting two output pulleys. The two input pulleys each comprise a fixed input sheave half and a moveable input sheave half and an effective diameter of each of the input pulleys is adjustable by axial movement of the moveable input sheave half relative to the fixed input sheave half. The moveable input sheave halves are controlled by a set of corresponding hydraulic cylinders. The fixed sheave halves are interposed between the hydraulic cylinders and the moveable sheave halves while the moveable sheave halves are interposed between the hydraulic cylinders.